1. Field of the Invention
Embodiments of the invention relate to industrial gas turbine exhaust systems, and more particularly to modular design, drop-in exhaust systems with a plurality of available enhanced exhaust flow path aerodynamic features, including, among others: flow path transition at the last blade row and diffuser interface inner and/or outer diameters; diffuser flow path angles that individually and severally in various combinations suppress flow separation and enhance pressure recovery; extended center body with a splined, compound curve tail cone or a multi-linear tail cone mimicking a splined compound curve; and turbine exhaust strut shapes with reduced trailing edge radius and increased manifold cast collar flow path radii. Embodiments of the modular drop-in exhaust system invention are also directed to enhanced structural integrity and serviceability features, including among others: last row turbine blade accessibility; turbine exhaust case (TEC) and/or turbine exhaust manifold (TEM) support struts with constant thickness vertical/radial cross section collars; modular support struts; single- or multi-radius, scalloped mounting flanges for fatigue resistance; enhanced mounting flange accessibility and mounting flange fastener replacement. The various features described herein may be utilized jointly and severally, in any combination.
2. Description of the Prior Art
Industrial gas turbine (IGT) exhaust system design often require balancing of competing objectives for aerodynamic efficiency, structural longevity, manufacture ease and cost, as well as installation and field service ease. For example, an IGT exhaust system designed to satisfy only aerodynamic objectives might comprise one or more metal castings/fabrications mimicking the construction of the compressor, combustor and/or turbine sections, airflow-optimized for the engine. That aero-optimized design casting/fabrication would not be readily adaptable to accommodate airflow parameters if other portions of the IGT design were modified. For example, the exhaust system would need to be re-optimized (with the expense of new castings/fabrications) if new turbine blade/vane designs were incorporated into the engine. Only specific portions of the aero optimized design castings/fabrications might experience thermal damage necessitating replacement after service, while other portions might not experience any discernible wear. Replacement of the entire exhaust as a repair solution for only localized wear would not be cost effective. A more desirable manufacturing and/or service repair solution would be creation of an exhaust system design (including, by way of example, a modular exhaust system design) that facilitates replacement of worn portions and periodic upgrades of the system (including upgrades to increase exhaust system longevity and durability as their needs are recognized over time) without requiring redesign and fabrication of an entirely new exhaust. Exhaust system manufacturing and service objectives include ease of initial manufacture, installation, field repair and upgrades during the service life of the IGT engine with minimal service downtime, so that the engine can be utilized to generate power for its electric grid.
Some known IGT exhaust designs are shifting to so-called single piece exhaust systems (SPEX) that in some cases facilitate drop-in connection to the turbine section. Some of these SPEX designs couple a generally annular turbine exhaust case (TEC) to the downstream portion of the IGT engine turbine section, and in turn couple a separate turbine exhaust manifold (TEM) to a downstream end of the TEC. Both the TEC and TEM have diffuser sections that mate to each other and when so mated form inner and outer exhaust cases. The turbine exhaust path is formed between inner facing opposed surfaces of the inner and outer exhaust cases. For ease of manufacture the TEC and TEM diffuser sections that form the inner and outer exhaust cases are fabricated primarily from welded sections of rolled steel that are structurally separated by outwardly radially oriented struts having airfoil cross sections. The inner and outer exhaust cases sections generally comprise serially joined cylindrical and frusto-conical sections with generally sharp angular changes between the sections, due to the relatively small number of joined sections. Sharp angular changes do not generally foster smooth laminar exhaust airflow and encourage boundary flow separation, leading to energy wasting turbulence and backpressure increase. While smoother airflow would be encouraged by use of more gently curving interior surface annular constructions, they are relatively expensive to produce given the large diameter of IGT exhausts. Also as previously noted, it is expensive to fabricate new casting/fabrication designs necessitated by changes in the IGT flow properties (e.g., new turbine blades airflow properties) or other need to upgrade (e.g., for improved exhaust longevity). It would be preferable to construct IGT exhaust systems from modular components that can be reconfigured and assembled for optimization of changed IGT flow properties rather than having to create an entirely new exhaust system design when, for example, changing turbine blade designs.
Thus, a need exists in the art for an industrial gas turbine drop-in exhaust system with modular construction that facilitates design changes for any one or more of enhanced aerodynamics, structural integrity or serviceability, for example for optimization of exhaust flow when changing turbine blade designs.